While many factors are involved in precipitating relapse in recovering drug addicts, life stressors are often reported as a reason for the return to drug use. Methamphetamine abuse is on the rise yet little in known about the potential role of stress in relapse with this drug of abuse. We found that rats with a history of methamphetamine self-administration show increased drug seeking following up to 51 days of forced abstinence and these animals remain vulnerable to stress-induced relapse throughout this period. In addition, rats with a history of methamphetamine use show a time dependent increase in drug seeking following exposure to drug cues, We are currently exploring how methamphetamine exposure effects the neural circuits that may mediate the rewarding aspects of methamphetamine and how relapse provoking effects of cues may interact with this circuitry. In our preliminary experiments rats self-administered methamphetamine over the course of two weeks and we collected brains for analysis following 18 hours or 30 days of withdrawal from drug use under basal conditions or following exposure to drug related cues. We found that dopamine transporter mRNA was elevated in the substantia nigra after 1 day of withdrawal but returned to basal levels by 30 days. The same pattern occurred for tyrosine hydroxylase mRNA in the substantia nigra and ventral tegmental area. Western blots revealed that TH protein level was stable in the nucleus accumbens across time and drug treatment, however, TH levels in the ventral tegmental area were higher following 1 day of withdrawal compared to the 30 day time point in methamphetamine experienced rats. Corticotropin releasing factor mRNA levels were unchanged in the central nucleus of the amygdala, bed nuclei of stria terminals, and paraventricular nucleus of the hypothalamus across all conditions. We are currently analyzing brains from rats that showed methamphetamine seeking following exposure to drug associated cues and performing experiments designed to determine the effects of methamphetamine on the stress response. Through these experiments we endeavor to understand how drugs of abuse change the brain and why stress may lead to relapse.
| Shepard, Jack D; Chuang, David T; Shaham, Yavin et al. (2006) Effect of methamphetamine self-administration on tyrosine hydroxylase and dopamine transporter levels in mesolimbic and nigrostriatal dopamine pathways of the rat. Psychopharmacology (Berl) 185:505-13 |
